The present invention relates to a new prosthesis for a knee joint.
This prosthesis has the particular aim of providing a device
the funds for
optimal contact, stabilization and guidance between
the moving parts in the course of the three-dimensional movements
remembers that a knee prosthesis is an implant that is used for
surgical replacement of a damaged knee joint.
A knee prosthesis includes bone-related elements, which are generally metallic, and sliding elements generally made of a plastic material such as polyethylene. The metallic elements are:
- A femoral part that approximately reproduces the shape of the femoral joint of the knee; it is connected to the bone, either directly over a rehabitable surface, indirectly through the detour of an acrylic resin;
- - a tibial surface, which is connected to the upper end of the tibia (tibia), be it directly, be it by means of an acrylic resin; and
- - A rotula surface, which is connected to the posterior surface of the Rotulaknochens, be it directly, be it by means of an acrylic resin.
Metal parts are generally made of chromium-cobalt, titanium or
Stainless steel or other metals and alloys, in particular
Parts for gliding and steaming,
which separate the metallic parts are generally made
polyethylene; you can
either connected to the tibial part or the fixed plateau or
with respect to the latter being movable with a variable one
Degree of mobility in rotation (horizontal plane), in the
Anterior-posterior displacement (sagittal plane) and medial-lateral displacement
(Frontal plane); be they fixed or mobile, the sliding parts called "inserts"
made of polyethylene are articulated with the femoral part over two
connected, the inner and the outer, the
a certain congruence with the respective two concave surfaces of the
Polyethylene insert, called the acetabular depressions
become. A prosthesis is called "with
movable plateau ",
when the insert has free axial rotation. The prosthesis
according to the invention
is preferably of this type.
free axial rotation is a logical consequence of congruence, the
Congruence is a bigger tribological one
Advantage, thanks to which the pressures
and the wear of the polyethylene forming the insert low
are what a longer one
Lifespan of the prosthesis brings with it.
In the most recent forms of prosthesis, the support is performed over three surfaces with a third support zone located between the two condylar heads in contact with a median projection located on the upper surface of the insert. The interlocking of these two sections can mean:
- Either a third femoral condyle in a third cavity of the upper surface of the insert,
- - or an elevation in the upper surface of the insert in a cavity (housing) located between the two femoral joint heads;
- - or different shapes of cams, which sit between the femoral articular heads and rest on a ridge on the upper portion of the insert.
Of course, there are angles in a plane of the cut surface, which
makes the contact between the parts discontinuous.
Anterior section of the femoral prosthesis (trochlea) pivots by means of
a medallion made of polyethylene with the rotula. This medallion
made of polyethlyene is connected to the rotula base, or it may be related to
to be mobile on this latter. There is a certain congruence
between the femoral joint and the curl joint.
Knee prosthesis does not have the exact shapes of an anatomical joint
play. In fact, in the latter represent the Menisci
the congruence between the femoral and tibial parts. The cruciate ligaments and
the lateral ligaments
Keep these parts together and put in cooperation with the
asymmetric shape of the joint surfaces in a relative motion
the three levels of space (frontal, sagittal and horizontal) safely.
Because these different anatomical elements in the knee prosthesis
are absent, the latter has three types of requirements
the physiological requirements, the tribological requirements
and the requirements of stability.
(1) Physiological requirements
The physiological requirements of the knee must be respected and, in particular, the respective movements and positions of the femur with respect to the tibia: rolling / sliding with the return of the point of contact of the femur on the insert during flexion (90 °) and advancement of the femur during extension ( 0 °), which determines the moment of action of the rotulase tendon, which controls the effectiveness of the muscle drive and, via this detour, the comfort of the patient, the quality of the walking, ascending and descending stairs, rising from a low position. These references must be ensured in the course of the movements by the shape of the articular surfaces of the prosthesis parts (determined by the design of the prosthesis) and in particular by a cam effect between the femur and the insert in cooperation with a balanced tension of the lateral ligaments of the knee joint, determined by the act of the surgeon and by an auxiliary instrumentation that respects this requirement.
(2) Tribological requirements
be respected, so that the contact between the metallic
Femoral parts and the tibial and rotula inserts made of polyethylene none
Producers of phenomena of deterioration of polyethylene are. Especially
the contacts as congruent as possible
be because selective, linear or weak-area contacts producers of a
Pressure in the polyethylene and thus of wear and creep of the
the latter are.
In certain forms of prostheses, the polyethylene insert is fixed with respect to the tibia. In this case, the tangential movements of rolling / sliding, shearing, and all rotational movements in the contact zone between the femoral joint heads and the tibial joint pans are discontinued. Since the contacts are weak, increased pressures can be achieved at the level of the polyethylene. The designers' recommendations generally advise to respect a pressure less than or equal to 10 MPa in the zones of polyethylene where the overlay is constant, ie in the zones near the walking position. An ideal pressure of 4 MPa is desired. In the prostheses with a weak congruence (linear or puncture joint surfaces between the femur and the polyethylene insert), however, pressures above 30 MPa are often measured, which can even reach 50 MPa. This leads to a rapid degradation of the polyethylene, which may require further interventions to replace the prosthetic implants. A contact surface of more than 400 mm 2 is recommended. The prior art has resulted in the field of prosthetic joints to produce prostheses, the inserts of polyethylene are congruent with respect to the femoral surface, this congruence has the logical consequence that the insert with respect to the tibial base in the rotation must be movable , These implants are called moveable plate prostheses. In these cases, joint congruence can be respected, allowing for increased surface area contacts. With this type of prosthesis, pressures of the order of 4 to 8 MPa in the polyethylene are often obtained, which favors the life of the latter.
There are several congruent prostheses, but all have two major disadvantages that the present invention seeks to correct:
- - The contact congruence between the condylar and the tibial articular pans exists mainly near the extension, but decreases in the course of the diffraction;
- - congruence is planned only in a single plane: the sagittal plane; Thus, increased stresses may occur in the contact zones upon movements of tilting or rolling, turning, or a combination of these three directions, especially if the surfaces have angles.
to remedy this
the different surfaces
tangential to each other in the two spatial planes (sagittal and frontal)
be to glide without sudden stops and without corner contacts in
to enable the three directions.
(3) The stability requirements
Respect for the stability of the knee bearing a prosthesis can be achieved through various mechanisms:
- - Preserve the two cruciate ligaments;
- - preservation of only the posterior cruciate ligament, but it has been shown that in this case the anterior-posterior movement does not take into account satisfactory kinematics;
- Finally, stabilization of the prosthesis by a central mechanism designed to guide the femur with respect to the tibia.
last type of mechanism is actually the most effective to the
with the kinematics of the knee, and there is a device
of this type, which relates to the present invention.
The state of the art in this area suggests several types of mechanisms:
- The most classical is that of a pole that comes into contact with a vertical central block of variable shape;
- Other mechanisms rely on a cam cooperating with a central stop having a profile complementary to this cam, eg the third central femoral head located between the two lateral rod ends;
- - In other prosthesis assemblies may be a third central condyle, which is itself in the form of a transverse cylinder, which engages in the form of a cam in a transverse cylinder which terminates in its anterior portion.
This latter construction has, as a detrimental effect, the complete absence of the anterior post freedom of movement between the femoral part and the tibial insert when the cylinder has the same transverse axis as the two lateral rod ends. It is thus a mechanism of the so-called hinge type, which may be responsible for increased pressures at the level of the joint between the rotula and the femur. The mechanism of rolling / sliding is not respected, and one of the consequences may be the presence of severe rotula pain. The recovery of a certain mobility front / rear in the contact zone between the polyethylene insert and the tibial plate is not sufficient to compensate for this disadvantage; this mobility, which is at a different level from the normal level, produces a parasitic, "roll-forward" movement, during which the tibia recedes on flexion with respect to the femur, which can cause dislocation of the prosthesis parts.
a structure of this type of prosthesis (see WO 98/46171 A) contains the central projection
on its upper surface
a leading one
Curve on a complementary
rests, which lies between the two rod ends, creating a cam effect
which is optimal movement of the femur with respect to the tibia
developed. The intervention of this device in the frontal plane
However, it returns a broken curve, the source of bumps, of
Corner contacts ("edge-contact"), from hard stops, and
therefore, by mechanisms involving a relaxation of the prosthesis
The present invention is therefore based on a movable prosthesis
Plateau, with the plateau or the insert in the transverse
Direction on its upper surface
with the articular surfaces
of the femur and with its lower surface with the upper surface of the
metallic base implanted into the tibia is completely congruent.
show the currently existing prostheses with movable plateau
most of the congruence in the zones close to the stretch, but
this congruence diminishes considerably during the
Diffraction due to the progressive reduction of the radii of the
Condyle curve in the posterior portion of the joint, while the
Curve radius of the tibial plate remains constant. That is due to
the polycentric radius of the condyle in the sagittal plane.
Implants have contact surfaces that
are increased from the extension to the diffraction. In these versions
However, the different sagittal planes (in the plane XY) are against each other
moved, resulting in a broken front view
the one for that
To generate load peaks at the level of polyethylene as well as transmissions
of abnormally high loads, shocks, and vibrations on the
Attachment points of the prosthesis during the movements of rolling /
Generally, the circulation of the knee prostheses happens through the contact
between the femoral joint heads
and the tibial articular pans with a medial overlay and a
lateral support. Because the mechanical axis of the body, the
from the center of gravity of the body
to the contact of the foot
goes to the ground, with respect to the knee joint runs in a medial manner, are
the pads on the two areas of the knee (medial and lateral) asymmetric,
which creates multiple sources of problems:
of it is the fact that created a moment of relaxation
is caused by a pressure in the internal area, which is significantly higher than
a pressure in the outer area.
Therefore, the outer area has
The knee has a tendency to reach the level of its tibial attachment
to lift and a possibility
of the latter, which is a source of mobilization
Denture is what causes deterioration and a new surgical
other source of problems lies in the fact that between
the support phase
and the vibratory phase is a step of detaching the metallic femoral part
with regard to the use of polyethylene, which is called in English "lift-off" and the man
translate with "roulis" effect
can. This "lift-off" occurs mainly between
40 and 70 ° knee flexion
on, especially in the range 50 to 70 °. It is generally about
of the lateral condyle with respect to the lateral tibial plate.
This "lift-off" physiological on
Way (about 1.8 mm) may exist, in certain cases of prostheses amplitudes
reach of several millimeters, even 5 mm or more.
that according to the invention
elaborated form of circulation happens the circulation by the detour of the
concave-convex meshing in the frontal and sagittal plane
through the lateral rod ends
on the central tip as well as on the lateral oblique sides
this dome, what, how later
will see one of the major orginalities of the present invention
In the concept proposed according to the invention, the resultant of the transmissions of the loads preferably occurs in the middle portion of the tibial base around its central cone-shaped fastener inserted in the middle of the upper end of the tibial bone. This kind of transfer has The aim is to maximally reduce the effect of the mediallateral moment which is responsible for the relaxation or also for the predominant wear on one of the two areas.
concave-convex engagement in the frontal and sagittal plane between
the central depression of the femur and the torus (the middle
Insert) offers the advantage in the course of the lift-off movement
from the flexion angle of the knee a congruent and progressive
Edition to offer.
Form of contact between the metallic femoral part and the
Polyethylene insert allows
the contacts in a continuous manner through progressive intervention
the contact surface
let while avoiding shocks and
Vibrations, which, when attached to the anchorages of metal parts
in which tibial or femoral bone are transmitted, source of
There are vibrations that continue there loosening of the prosthesis parts
which leads to a replacement of the latter.
The present invention aims to propose a knee prosthesis which does not have the above-mentioned disadvantages of the prior art prosthesis. The prosthesis according to the invention has two aims:
- The congruence designed to protect the longevity of the polyethylene used and to reduce wear;
- - A kinematics, which is intended to give the patient a comfortable functioning.
- - One
Congruence with a big one
Contact area between
the femoral part and the insert regardless of the diffraction angle
it to reduce the pressures exerted on the polyethylene;
- - The
Congruence must decrease in the course of diffraction, with the large contact area in the support area
from 0 to 60 ° required
but the bending range beyond 90 ° does not require a large contact area,
Use of this area is very rare;
- the up
all diffraction angles, in particular extended beyond 90 °
Congruence a very limited
Prosthesis and therefore a risk of excessive loading of the anchorage;
- the congruence
from the diffraction angle is required, but without corner contact and
without flattening zone or direction reversal of pin and hole type, the
engage the movements of the lift-off or lateral inclination:
that is the frontal congruence.
- - The
Kinematics must favor the lever arm of the stretching device
(Work efficiency of the quadriceps muscle by means of the rotula
and the Rotula tendon) to be an effective force during the
To ascend and descend stairs.
This is due to an anterior shift of the rotula support
the trochlea achieved in the stretching.
- - The kinematics must respect the real rolling / sliding of the knee. This is defined in the following way: the contact point of the femoral part with respect to the insert, when stretched at 0 °, is a few millimeters before the center of this insert, and it retreats a few millimeters behind the center of the insert, when the diffraction 15 to 20 ° without the femoral part and the femoral bone segment moving backward with respect to the tibial part or the tibial bone segment. This differs from the false rolling / gliding, in which the femoral part and the femoral bone retreat by a cam effect with respect to the tibial part of the prosthesis or tibial bone, a phenomenon which must be avoided because it is a producer: 1. Increase from abnormally Pressing on the polyethylene of the rotula and the insert, source of premature wear and pain; 2. translational movements of the femur from front to back on the insert, causing delamination below the surface of the polyethylene and thus premature wear of the latter.
To address these goals, the present invention proposes a new geometry of the surfaces of the femoral part and insert. More particularly, the invention relates to a knee joint prosthesis which includes:
- A system with three support zones between the femoral part and the insert;
- A system with a continuity of contact between the bearing surfaces of the femoral part and the insertion mediallateral;
- A concave-convex succession of surface segments;
- In the frontal plane, a succession of engagement femoral component insert concavo-convex, then convex-concave, then concave-convex, starting from the medial section to the lateral section;
- In the sagittal plane, the three femoral surfaces (medial, central and lateral) have a convexity directed downwards, while the three surfaces of the insert have an upward concavity so that one has a central zone in the form of a saddle, but a continuous mediallateral contact.
Invention has alike
to propose a knee prosthesis in which the general
Form of the three zones (lateral, central and medial) of the femoral part
is determined by a spiral curve in the sagittal plane, wherein
the general shape of the three zones (lateral, central and medial)
of use alike
is determined by a spiral curve in the sagittal plane, where
the generating spiral curve of the insert from the generating spiral curve
derived from the femoral part. These two spiral curves will be
calculated with the aim of real rolling / gliding according to the above
To reproduce definition.
Invention has alike
to the goal a knee prosthesis, in which the congruence of the articular surfaces between
the femoral part and the deployment at the frontal level
is due to a succession of continuous curved surfaces on the
Level of the three support zones, with the curved surfaces are interconnected
without any discontinuity
or sharp edge or direction reversal line or flattening, causing
thus a movement in rolling in translation and in inclination in
the frontal plane between the femoral part and the insert is made possible
in the course of which the contact area
from the diffraction angle is always congruent. In the sense of the present
Invention is believed that the surface of the prosthesis is a flattening
when, in one of its points, the surface of the prosthesis is more than
one millimeter at least three tangents to this surface,
which define a plane.
Invention finally has
To the goal of a knee prosthesis, in which the pads in a continuous manner
transferred from the medial part to the lateral part of the prosthesis
be in the course of the cycle of walking with a bum-free
Stress without risk of vibration or sudden transmission of stress,
the patient has an effect of pleasant suppleness
is avoided and that he feels shocks.
To this end, the object of the invention is a knee prosthesis of the type comprising a generally metallic femoral part suitable for implantation in a femur, a generally metallic tibial part suitable for implantation in a tibia, and Includes intermediate part or insert of a plastic material such as polyethylene, which is inserted between the femoral part and the tibial part, wherein the insert can be fixedly connected to the tibial part or rotatable about a vertical axis relative to this movable, the femoral part on the one hand contains two Seitenab sections, the be adapted to rest and move in two lateral recesses of the corresponding profile of the insert and, on the other hand, a recessed central portion which is arranged between the side portions and adapted to take on a projecting central part of the insert receiving the projecting middle section the femoral part facing surface of the insert from the front to the back of the insert seen from the front has a convex shape and seen in profile a concave shape, while the central portion of the femoral part from its front to its back seen from the front of a concave shape and Seen in profile has a convex shape, which allows him to ride in the course of its relative movements on the projecting portion of the insert and cooperate with him in the manner of a cam, said prosthesis being characterized in that
- The surfaces of the femoral part and the insert, which are called to come into contact in the course of the relative movements of the two parts, have no discontinuity or edge and by overlapping of concave portions and convex portions in the course of their movements in each of the sagittal - and frontal levels to cooperate;
- - The surface of the insert, which faces the corresponding surface of the femoral part, in a section in a frontal plane is a curve having a wavy center portion in the form of a saddle, the convexity of which faces the femoral part and on each side to a recess portion and having a shape substantially corresponding to that of the associated portion of the femoral part, the whole forming a wave curve without discontinuity or edge of the general type of sinusoid so that in section in a frontal plane the surface of the femoral part corresponding to the corresponding surface of the femoral part Turning the insert faces and medial-lateral is in continuous contact with the latter, is a curve having a corrugated central portion, whose concavity faces the insert and which connects on each side to side portions of the femoral part, the whole a wave curve without discount inuity or sharp edge of the general type of sinusoid.
In this prosthesis, the femoral surface is formed starting from a spiral curve in the sagittal plane passing through a wave pattern of sine wave in the frontal plane, and the surface of the insert is formed from a spiral curve in the sagittal plane which is a sinusoidal wave curve in FIG the frontal plane passes through, with the two surfaces in each of the two levels form a concave-convex engagement.
The surfaces of the femoral part and the insert which are called to come into contact with each other in the course of the relative movements of the two parts are thus portions of the surface which have no discontinuity, edge, flattening or zone of reversal of direction and which overlap the concave ones Sections and the convex portions interact independently of the diffraction angle in the course of the totality of movements in both the sagittal and in the frontal plane. The surfaces of the femoral part and insert, which are arranged in relation to each other, are intended to allow the movements:
- In a frontal plane: a so-called "lift-off" movement, ie the sliding lifting and angling of one of the side portions of the femoral part, whereby a contact between the femoral part and the insert remains congruent both in the lateral depression of the insert and independent of the diffraction angle on the whole or a portion of the central projection of the latter;
- In a sagittal plane: a diffraction movement preferably with a real rolling / sliding of the femoral part on the insert, ie a shift of the contact point of the femoral part on the use of a few millimeters before the center of the insert in the extended position 0 to a few millimeters behind the middle the insert in the flexed position, but without displacement of the femoral part itself or the bone segment that it carries with respect to the tibial part (absence of translation);
- In a horizontal plane: rotation with respect to a vertical axis whose amplitude varies, according to whether the insert is movable in rotation with respect to the tibial part or not; According to the invention, the insert is preferably free in the axial rotation.
of the insert facing the corresponding surface of the femoral part
is and in the medial-lateral direction (transversal) in continuous
Contact with the latter stands, in sectional view in a frontal plane
two lateral curve sections with an upward
and a middle curve portion whose convexity to the
Femoral part is directed, with the convexity of the middle section
on each side connects to the concave sections with a profile that
essentially the corresponding lateral portion of the femoral part
corresponds, with the whole from the front to the back
Using a curve without discontinuity or edge or flattening
forms, which resembles a sine wave.
has the femoral part from the front to the back
its side sections into a sectional view in a frontal plane
a complementary one
Profile on. In other words
is there a medial convex curve that is directed downwards,
then a central concavity,
which overlaps the central portion of the insert, then a lateral convexity that follows
is directed downward, these three curve segments in the medial-lateral direction (transversal)
in continuous contact with the corresponding surfaces of the
Prosthesis of the former
Technique (see U.S. Patent No. 4,470,158) also contains a femoral part,
which is formed by two generating curves, a frontal curve,
which goes through a sagittal curve.
However, prosthesis differs fundamentally from that of the application in that
that the frontal generation curve is a geometric element of the
Design is, but not at all
a contact zone between the prosthesis parts (femur and insert)
equivalent. In fact, the femoral part of this prosthesis only has
the two classic rod ends
separated by a discontinuous zone (an incision)
are, while according to the present
Invention a total continuity
from one side of the femoral part to the other.
in this US patent is the section of the production curve called K3
an element of the design, but not a zone of a continuous one
Matter and an edition of the femoral part on the insert
as in the prosthesis according to the invention.
The frontal production cowl of the US prosthesis passes through a
polycentric sagittal curve, the four segments with different
Contains radii from front to back, while according to the present invention
the frontal curve passes through a spiral generating curve.
In another prior art prosthesis (U.S. Patent No. 5,609,639 to Walker), a femoral part has continuity in the portion located between the two "condylar heads" and comes into contact with a "meniscal" component that has a central one curved portion, the convexity of which faces the femoral part and is connected to two lateral recessed portions. However, it is shown that the femoral portion has a constant radius in the sagittal plane and that the "meniscal" component either has a constant sagittal radius, with front to back mobility occurring between the meniscal component and the tibial plane, or a variable sagittal radius defined by the impression of movements from the front to the back, impressed by the femoral part on the constant sagittal radius. This can neither the forms nor any of the functions the movement or contact that is possible by the intervention of a spiral in a spiral.
In the frontal plane, the femoral part of the Walker patent has a "condyle" (and hence anatomical) shape and conformance to the lateral depressions of the meniscal component (also anatomical), which distinguishes it from the present invention. In this patent, no geometrical description is given of the contacts in the middle section between the femoral part and the "meniscus" component except through continuity of the contact. When you look up 3 (b) and 3 (c) According to this patent, it is noted that in the posterior portion of the insert there is a flattened center zone which adjoins the side sections via angled edges, which is incompatible with the properties of the surfaces of the femoral part and the insert according to the present invention, and with Figs kinematic and tribological benefits that follow. Likewise, the trochlea of the femoral part is the 3 (b) flattened and contains in its central portion no concave-convex shape. It must therefore connect with angles to other surfaces.
still according to the earlier technique
Patent FR No. 2,621,243 a prosthesis whose tibial part in his
Middle section has a shape of a horse saddle, wherein the
Femoral part only about
a punctual contact with the Tibialteil comes into contact and
only on the middle section, without any contact between the side sections of the
Femur and the tibial element gives. Also, the shape of the tibial saddle
in the sagittal plane simply convex and will not go through a curve
defined by the type of a spiral. So it does not have the benefits
the with the intervention of a spiral into a spiral during the diffraction
of the knee is connected about a transverse axis.
The practice is in the prosthesis according to the present invention
the exact shape for the
Spiral curves of the insert and the central surface of the femoral part in the
Sagittal plane is assumed, starting from radiographs of the knee
of the patient defined in different diffraction positions, so
that as accurate as possible
the shift of the contact point of the natural joint in the real one
Rolling / sliding is reproduced, i. a shift of the contact point
without displacement of the bone segments or prosthetic components.
will be the exact shape for
the curve in the frontal plane should be assumed by the
Necessity of tilting about 5 ° between the femoral part and
the use defined in the "lift-off" lateral
Take off (or varos-valgus).
distinguishes the prosthesis according to the invention
from that of WO 98/46171 A, in which, even if a continuity with three
Support surfaces exists
(two rod ends
and a cam between the rod ends), the conformity in the
Frontal plane only the lateral recesses of the insert and the
corresponding "rod ends", but not
the middle section.
Schematic drawings illustrate in more detail
the invention. Of course you have no
Properties. In these drawings:
is 1 an exploded perspective view of a knee prosthesis according to the invention;
is 2 a schematic view on a larger scale, showing the substantially complementary shape of the contact surfaces with respect to the insert and the femoral part; and
shows 3 Sections of the contact surfaces with respect to the insert and the femoral part in a frontal plane.
By 1 shown knee prosthesis contains a generally metallic femoral part 1 , which is suitable for implantation in the femur of the patient, also a metallic tibial part 2 , which is suitable for implantation in the tibia of the patient, and an insert 3 which is generally made of a plastic material such as polyethylene.
The use 3 lies on a plateau 4 of the tibial part 2 and, as shown in the design, may be rotatably movable with respect to the platform about an axis that is vertically disposed in the position of use of the prosthesis. For this purpose, the insert contains 3 projecting from his part here 2 facing surface of a survey 5 , in a known manner in a central hollow cone 6 of the tibial part 2 intervenes.
In the usual way, the femoral part contains 1 two side sections whose cross-section, in section in a sagittal plane, is in the form of a coil whose exact mathematical equation is foreign to the present invention.
The femoral part 1 is intended to be preferably in accordance with a rolling / sliding movement of the side portions 7 on recessed sections 8th the part 1 facing surface of Einsat zes 3 to move, which have substantially corresponding shapes, also with a profile of a turn, seen in section in a sagittal plane.
According to the invention, the use 3 in its middle section a projecting spine section 9 on, which forms a cam, seen from the front (s. 2 and 3 ) has a corrugated profile, the convexity of which faces the femoral part, while having a concave profile in the form of a saddle, seen from the side, this projecting portion 9 has no discontinuity, angle, or edge and tangential in all directions also without discontinuity, angle or edge to adjacent surfaces 8th followed. The section 10 of the femoral part 1 has a substantially complementary shape to that of the section 9 the insert, which it superimposes from the extension to the full inflection, and also closes tangentially in all directions without discontinuity, angle, flattening or edge to the side sections 7 at.
median concavo-convex intervention allows the same
Stopping abnormal movements (subluxation or dislocation) to the front
or to the back
of the femur with respect to the tibia or vice versa with the advantage
this stopping because of the continuity of the surfaces in the
The exact shape of the cam forming projecting portion 9 in the sagittal plane is determined by going to radiographs of the knee joint, which is angled in large numbers of different positions, and it is not defined by an exact mathematical equation. This cam is such that at a diffraction angle of 0 °, the femoral part support center on the insert is a few millimeters before the center of the insert, and from a certain diffraction degree, which is between 15 and 20 °, a few millimeters behind this center ,
each of the femoral part and the insert are easy in all levels
tangent to each other without any breaking zone, with the
from the front to the back
of the mission, as physiology wants.
2 Figure 4 shows the surfaces created for the femoral part contact surface by the two curves S1 and Spi F and the contact surface of the insert of S2 and Spi T.
As stated above, the curves Spi F and Spi T have the form of a spiral, without this term implying an exact mathematical definition. Likewise, in a section in a frontal plane, the contact surface S1 of the femoral part 1 and the contact surface S2 of the insert (s. 3 ) a sinusoidal profile without this term implying a precise mathematical equation.
It should be noted that the recessed middle section 10 of the femoral part 1 from front to back over a curve with constant radius R 2 to the side sections 7 this part 1 can connect. Likewise, the femoral part can 1 facing convex middle section 9 of the insert 3 from front to back over a curve of constant radius R ' 2 to the lateral recessed portions 8th connect this insert.
prosthesis according to the invention
has the advantage of increasing the physiological kinematics of the knee
respect, i. the preferred movement of rolling / sliding
of the joint with the retreat
the point of contact of the femoral part on the insertion of the extension
to the diffraction, what the action moment of the drive device
optimized and therefore the propulsive force of the knee at an increase,
a dismount and getting up.
It has the same advantage:
- To maintain an increased contact surface in the course of the flexion of the knee, which as a consequence causes a low pressure in the polyethylene and therefore a weak wear of the prosthesis;
- To preserve a congruence during the tilting movement in the frontal plane, and therefore an absence of bumps and mechanisms of severing or loosening;
- - To communicate this device a good stability of the parts to each other during the movements from front to back and the lateral inclination;
- - To preserve a surface of total medial-lateral contact from the extension to the full inflection, wherein the surface is continuously reduced by contacting the spiral curves.